1. Field of the Invention
The present invention relates to a disk drive apparatus, which at least reads signals from an optical disk recording medium, and a method for adjusting a focus bias and a spherical aberration correction value.
2. Description of the Related Art
The technologies for writing/reading digital data may include a data recording technology by using an optical disk (including a magnetooptical disk), such as a CD (Compact Disk), an MD (Mini-Disk) and a DVD (Digital Versatile Disk), as a recording medium.
There are a read-only optical disk as known as a CD, a CD-ROM and a DVD-ROM and an optical disk on which user data can be written as known as an MD, a CD-R, a CD-RW, a DVD-R, a DVD-RW, a DVD+R, a DVD+RW and a DVD-RAM. Data can be written on the writable optical disk by applying a magnetooptical recording scheme, a phase-change recording scheme, a dye film change recording scheme and so on to allow recording data. The dye film change recording scheme may be also called “write-once recording” and is suitable for the application of data saving since data writing is allowed only once but rewriting is not allowed. On the other hand, the magnetooptical recording scheme and phase-change recording scheme allow data rewriting and may be applied for applications including recording contents data of music, video images, games, application programs and so on.
Furthermore, in recent years, a high density optical disk called “BLU-RAY DISC®” has been developed, and the capacity has been increased.
A high density disk such as “BLU-RAY DISC®” has a disk structure having a cover layer of about 0.1 mm in the direction of the thickness of the disk and writes/reads a phase change mark under the condition of the combination of laser (so-called blue laser) 405 nm wavelength and an objective lens with an NA (numerical aperture) of 0.85.
The recording capacity may be about 25 GB (gigabytes) on a disk 12 cm in diameter. The two-layer structure, for example, of the recording layer may allow the capacity of about 50 GB, which is the double.
By the way, as publicly known, a focus servo operation that controls the focal position of laser light on a disk recording surface and a tracking servo operation that controls laser light to trace a track (that is, a track by a pit array or a groove) on a disk are performed in an optical disk apparatus that writes/reads to/from an optical disk.
Then, with respect for the focus servo, it is known that applying a proper focus bias to a focus loop may be required for proper writing/reading and servo operations.
A high density disk may require spherical aberration correction in order to address the thickness error of the cover layer thereof and support the recording layer of the multi-layered structure. For example, those having a spherical aberration correction mechanism employing an expander or a liquid crystal element within an optical pickup have been developed.
A writable optical disk apparatus (recording/playing apparatus) including a high NA lens such as the “BLU-RAY DISK®” in particular may require the automatic adjustment of the focus bias and spherical aberration correction since the margins of the focus bias/spherical aberration correction are relatively narrow.
The method for adjusting a focus bias and a spherical aberration correction value is disclosed in JP-A-2004-241081 and JP-A-2003-233917 (Patent Documents 1 and 2).